Immunoglobulins are the key effectors of the humoral immune response. Correct immunoglobulin expression, which is limited to B lymphocytes and varies during B-cell development, is critical for normal immune function. Immunoglobulin heavy chain (IgH) gene transcription has provided an unusually informative paradigm for studying mechanisms which control the expression of highly regulated mammalian genes. Our work, in conjunction with that of others, has led to the identification of DNA elements responsible for the regulation of IgH gene transcription and to the cloning and characterization of activators which bind to specific sequences within these elements. Since the components of regulated IgH transcription have been identified, it is now possible to study how these components function to control the efficiency and frequency with which RNA polymerase II initiates transcription from VH promoters. The proposed studies focus primarily but not exclusively on three families of activators which we have studied in the past--those binding E, mu-E1 and mu-E3 sites. The roles of different family members and the mechanisms by which their availability and activity are regulated during B cell development will be studied. Components of the basal transcription machinery which are targets for these activators will be identified and co-activators which may be necessary for their action will be studied. The role of DNA bending in VH promoter activity will be determined and mechanisms required for activators to work from a distant (enhancer) site will be studied. Finally, the requirement for specific activators in lymphocyte function and in the development of whole animals will be determined using gene targeting experiments. The proposed studies are the logical culmination of previous work because we now possess the molecular tools necessary to dissect individual molecular events in the regulated transcription of IgH genes. Thus, studying IgH transcription will continue to provide paradigmatic new insights into transcriptional regulation in higher organisms.